Date: Fri, 8 Aug 1997 03:00:01 -0700 (PDT) From: tetsuya@secom-sis.co.jp (Tetsuya Furukawa) To: freebsd-bugs Subject: Re: kern/4243: file locking doesn't work for pipe Message-ID: <199708081000.DAA06716@hub.freebsd.org>
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The following reply was made to PR kern/4243; it has been noted by GNATS.
From: tetsuya@secom-sis.co.jp (Tetsuya Furukawa)
To: peter@spinner.dialix.com.au
Cc: dg@root.com, FreeBSD-gnats-submit@FreeBSD.ORG
Subject: Re: kern/4243: file locking doesn't work for pipe
Date: Fri, 8 Aug 1997 18:58:53 +0900
Since I remembered the proper specification of flock(), I also think
that flock() for a file descriptor shared among different processes
is obviously useless.
But fcntl() for a shared file descriptor may be useful because
fcntl() has the other specification.
In fact, the following program prints "fcntl works fine." on
FreeBSD 2.2-STABLE i386.
----
#include <sys/file.h>
#include <sys/errno.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
int
main()
{
int fd;
struct flock flbuf;
char c;
flbuf.l_start = 0;
flbuf.l_len = 0;
flbuf.l_type = F_WRLCK;
flbuf.l_whence = SEEK_SET;
fd = open("lockfile", O_WRONLY | O_CREAT, 0666);
if (fork() == 0) {
/* child */
fcntl(fd, F_SETLKW, &flbuf);
sleep(2);
exit(0);
}
/* parent */
sleep(1);
if (fcntl(fd, F_SETLK, &flbuf) == -1) {
if (errno == EAGAIN)
printf("fcntl works fine.\n");
else
printf("fcntl fails: %s\n", strerror(errno));
} else
printf("fcntl is discarded.\n");
return 0;
}
----
File locking for a pipe by fcntl() fails on FreeBSD.
I think the priority of supporting it is low.
To the developer of the Apache's module, I suggested to do fcntl()
for a temporary file.
--
Tetsuya FURUKAWA in Tokyo, Japan
PGP Key fingerprint = C2 86 A6 7C 72 A0 A1 94 F4 4C 83 9D D1 E3 47 BD
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